Belting is used today in many types of agricultural machinery, e.g. hay balers. A popular type of hay baler which is marketed today employs a plurality of belts which are used to form the hay into round bales. This type of baler is known as a round hay baler. The belts which are used on the round hay balers are typically in the order of 40 feet in length.
There are several factors which must be taken into consideration when designing belting for hay balers. One factor is that when a hay baler is making bales, the belts are stretched to heavy loads. These loads cause the belts to stretch and the amount that the belt stretches under the load must remain within a certain tolerance; otherwise the bale it is making will become too large, which interferes with proper baler operation.
The amount of stretch in belts used on hay balers is substantial. For example, a typical maximum specification for elongation of belts for hay balers has been 3% at a specified load. A 40 foot belt is thus permitted to stretch up to about 14 inches under that load. When the belt stretches beyond tolerable limits, the belt is removed and shortened. Shortening the belt is typically accomplished by trial and error techniques, especially in the fields. Such trial and error techniques can produce unsatisfactory results.
Manufacturers of hay balers have continued to increase the specification for the density of bales which a baler can produce. The amount of loading to which the belts of the baler are subjected to make denser bales is increased and hence the likelihood that a belt will stretch by an amount beyond tolerable limits for proper operation is increased. Another factor to be considered in belt design is the ability of the belt to flex in operation without the ply material cracking. In that regard, a typical round hay baler employs a plurality of rollers on which the belts are installed. The position of the rollers is such that the belts are subjected to a substantial amount of flexing in traveling around the rollers. Moreover, some of the rollers are positioned such that the belts must travel in an S-shape during operation. If the belts fail due to the flexing stress, the belt must be replaced to obtain proper operation of the baler.
Another aspect of the flexing problem is manifested at the location where the belt is spliced. A popular way to connect the ends of the belt is with the so-called "clipper splice" as shown in FIG. 3. The likelihood of belt failure due to flexing is most pronounced at the location in the belt in the vicinity of the clipper splice. This is because the plies of the belt are most prone to crack at the splice.
Yet a third factor which must be considered in belt design is the environment in which the belting is used. Belts used on agricultural equipment are subjected to severe environmental conditions and in this regard moisture is perhaps the greatest problem. If the ply material of the belting is deteriorated by moisture, the belt can fail in operation. It is seen that belting for hay balers needs to be dimensionally stable, able to flex without cracking, and not subject to environmental deterioration.
One popular belt that has been used on hay balers is a two-ply belt wherein the plies are made of a polyamide fabric, e.g. nylon. Polyamide fabrics are used in belts for hay balers, inasmuch as they have excellent flexing characteristics and are not susceptible to moisture deterioration as other materials. However, the elongation problem in such belts is pronounced since the polyamide material has a relatively high elongation modulus and also tends to stretch when wet. One proposed solution to the elongation problem in two-ply polyamide belts has been to initially make the belts shorter than required in order to compensate for elongation. Under this proposed solution, the assumption is that all belts will stretch in use to the proper length. This approach is not really sound nor acceptable since all belts on the hay baler do not stretch an exact amount. Even though unacceptable, this approach has been utilized in the industry to account for the elongation problem.
Another suggested solution is the use of two polyester fabric layers, especially in connection with belts having a high coefficient of friction surface. These fabrics, however, have proven to be incapable of withstanding the continuous shock loading encountered in the hay baler. The shock loading is due to the high degree of weight variation of the material being fed into the baler and the tumbling of a large mass of material weighing between 400 and 3500 pounds. The load has a continually changing center of mass due to the variable densities of the centrifically tumbling material within the baler, which adds to the stress on the belting. Finally, the aggressiveness of the contact made between the high coefficiency of friction surface of the belt and the material being fed into the baler places additional stress on the fabrics.
There have been other suggestions to solve the elongation of stretching problem in belts. One such suggestion was to make a two-ply belt where the plys were made of a rayon material. Rayon has a lower elongation modulus than a polyamide fabric and hence does not stretch as much as a polyamide belt of the same load. However, this belt proved to be unacceptable since rayon is particularly susceptible to moisture attack.
Another suggestion for solving the elongation problem was to make a two-ply belt, wherein the plies were made of a polyester material. This proposed solution was ineffective inasmuch as the polyester plys tended to crack when flexed, and cracking was most pronounced in the area of the clipper splice.
Another type of belting which was used on the hay balers included a three-ply belt, wherein the center ply was made of a polyamide fabric and wherein the outer two plys were made of cotton. However, moisture caused the cotton to rot and the belt then failed since it was not able to carry a sufficient load.
Still another type of belting employing a three-ply belt described in U.S. Pat. No. 4,371,580, issued on Feb. 1, 1983. The center ply of the belt comprises a first synthetic fabric and each outer ply comprises a second synthetic fabric. The modulus and flex fatique life of the second fabric are respectively greater than the modulus and flex fatique life of the second synthetic fabric. In general, the center ply comprises a polyester fabric while the outer plies comprise a polyamide fabric. While the three-ply belting of the patent 4,371,580 overcomes the problems encountered with previous beltings, the manufacture of a three-ply belt is relatively expensive when compared with the traditional two-ply belts heretofore used in the industry.